The circular dichroism (CD) is the phenomenon that the optical absorption characteristics of the sample to be measured with the right and left circular polarized light are different. CD spectrum is measured to measure the chirality of the optically active material (for example mineral compounds, organic compounds, biological molecules or the like) having chromophore.
In the conventional CD spectra measuring method, a light projected from a light source is dispersed into a monochromatic light by a spectroscope, the monochromatic light is linearly polarized by passing through a light polarizer, the linearly polarized light is circularly polarized by a polarization modulator such as a photoelastic modulator (PEM), and then the circularly polarized light is irradiated to a sample to be measured. The light irradiated to sample is absorbed by the sample according to an optical absorption characteristic thereof. A detector receives the light output from the sample. Then CD spectrum is calculated on the basis of an electric signal corresponding to alight intensity of the light received by the detector.
FIG. 8 is a schematic diagram of the CD spectra-measuring device according to the conventional method for measuring the CD spectra. In the FIG. 8, the numeral number 30 indicates a light source, 31 indicates a spectroscope, 32 indicates a light polarizer, 33 indicates a photoelastic modulator (PEM), 34 indicates a sample cell and 35 indicates a detector.